Evolution of femtosecond laser-induced damage in doped GaN thin films

Mg- and Si-doped GaN layers deposited by metalorganic chemical vapor deposition method were irradiated with femtosecond pulse duration laser of three different wavelengths 1,030, 515 and 343 nm. Both single and multiple shot laser induced damage thresholds of doped GaN layers were evaluated and discussed. The scanning electron microscopy employed with electron beam induced current and energy dispersive X-ray techniques were used to study laser damage morphology. It was observed that ablated area and laser-induced damage increased with irradiation fluence. The mechanism of damage generation by Gaussian beam profile laser was considered.     

Low temperature electronic transport in sputter deposited a-IGZO films

We report on the electrical properties of a-IGZO thin films prepared by reactive sputtering. Without oxygen injection, dc resistivity measured at room temperature is ρ_300K = 1.22 × 10⁻³ Ωm. The lowest resistivity ρ_300K = 4.86 × 10⁻⁵ Ωm is obtained at a certain oxygen supply into the deposition process. Hall effect measurements of these films reveal a metallic-like behavior from mobility and carrier concentration vs. temperature in the range 15–300 K whereas films deposited without oxygen or for the highest oxygen flows behave as semiconductors. These enhanced electrical properties are connected to the oxygen vacancies and the local coordination structure around the In³⁺ cations.     

Chemical triple-mutant boxes for quantifying cooperativity in intermolecular interactions

Chemical double-mutant cycles have been used to quantify intermolecular functional-group interactions in H-bonded zipper complexes in chloroform. If the same interaction is measured in zippers of different overall stability, the double-mutant cycles can be combined to produce a triple-mutant box. This construct quantifies cooperativity between the functional group interaction of interest and the other interactions that are used to change the overall stability of the complexes. The sum of two edge-to-face aromatic interactions (-2.9 +/- 0.5 kJ mol-1) is shown to be insensitive to changes of up to 13.7 +/- 0.2 kJ mol-1 in the overall stability of the complex. In principle, enthalpic cooperative effects caused by entropy-enthalpy compensation could perturb the measurement of intermolecular interactions when using the double-mutant cycle approach, but these experiments show that, for this system, the magnitude of the effect lies within the error of the measurements.     

Photosynthesis-Inhibiting Activity of N-(Disubstituted-phenyl)-3-hydroxynaphthalene-2-carboxamides

A set of twenty-four 3-hydroxynaphthalene-2-carboxanilides, disubstituted on the anilide ring by combinations of methoxy/methyl/fluoro/chloro/bromo and ditrifluoromethyl groups at different positions, was prepared. The compounds were tested for their ability to inhibit photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts. N-(3,5-Difluorophenyl)-, N-(3,5-dimethylphenyl)-, N-(2,5-difluorophenyl)- and N-(2,5-dimethylphenyl)-3-hydroxynaphthalene-2-carboxamides showed the highest PET-inhibiting activity (IC₅₀ ~ 10 µM) within the series. These compounds were able to inhibit PET in photosystem II. It has been found that PET-inhibiting activity strongly depends on the position of the individual substituents on the anilide ring and on the lipophilicity of the compounds. The electron-withdrawing properties of the substituents contribute towards the PET activity of these compounds.     

Simultaneous determination of perfluoroalkyl phosphonates, carboxylates, and sulfonates in drinking water

A trace analytical method based on high performance liquid chromatography coupled to quadrupole time-of-flight high resolution mass spectrometry was developed for simultaneous determination of perfluoroalkyl phosphonates (PFPAs, carbon chain lengths C6,8,10), perfluoroalkyl carboxylates (PFCAs, C5-12), and perfluoroalkyl sulfonates (PFSAs, C4,6,8,10) in drinking water (tap water). Analytes were enriched on a mixed mode co-polymeric sorbent (C8+quaternary amine) using solid phase extraction. Chromatographic separation was achieved on a Zorbax Extend C18 reversed phase column using a mobile phase gradient consisting of water, methanol, and acetonitrile containing 2mM ammonium acetate and 5 mM 1-methyl piperidine. The mass spectrometer was operated in electrospray negative ion mode. Use of 1-methyl piperidine in the mobile phase resulted in a significant increase in instrument sensitivity for PFPAs through improved chromatographic resolution, background suppression, and increased ionization efficiency. Method detection limits for extraction of 500 mL tap water were in the ranges of 0.095-0.17 ng/L, 0.027-0.17 ng/L, and 0.014-0.052 ng/L for PFPAs, PFCAs, and PFSAs, respectively. Whole method recoveries at a spiking level of 0.5 ng/L to 500 mL HPLC grade water were 40-56%, 56-97%, and 55-77% for PFPAs, PFCAs, and PFSAs, respectively. A matrix effect (signal enhancement) was observed in the detection of PFPAs in tap water extracts, leading to calculated recoveries of 249-297% at a 0.5 ng/L spiking level. This effect resulted in an additional improvement of method sensitivity for PFPAs. To compensate for the matrix effect, PFPAs in tap water were quantified using matrix-matched and extracted calibration standards. The method was successfully applied to the analysis of drinking water collected from six European countries. PFPAs were not detected except for perfluorooctyl phosphonate (PFOPA) at close to the detection limit of 0.095 ng/L in two water samples from Amsterdam, the Netherlands. Highest levels were found for perfluorobutane sulfonate (PFBS, 18.8 ng/L) and perfluorooctanoate (PFOA, 8.6 ng/L) in samples from Amsterdam as well as for perfluorooctane sulfonate (PFOS, 8.8 ng/L) in tap water from Stockholm, Sweden.     

Investigating the spectrum of biological activity of substituted quinoline-2-carboxamides and their isosteres

In this study, a series of thirty-five substituted quinoline-2-carboxamides and thirty-three substituted naphthalene-2-carboxamides were prepared and characterized. They were tested for their activity related to the inhibition of photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts. Primary in vitro screening of the synthesized compounds was also performed against four mycobacterial species. N-Cycloheptylquinoline-2-carboxamide, N-cyclohexylquinoline-2-carboxamide and N-(2-phenylethyl)quinoline-2-carboxamide showed higher activity against M. tuberculosis than the standards isoniazid or pyrazinamide and 2-(pyrrolidin-1-ylcarbonyl)quinoline and 1-(2-naphthoyl)pyrrolidine expressed higher activity against M. kansasii and M. avium paratuberculosis than the standards isoniazid or pyrazinamide. The most effective antimycobacterial compounds demonstrated insignificant toxicity against the human monocytic leukemia THP-1 cell line. The PET-inhibiting activity expressed by IC(50) value of the most active compound N-benzyl-2-naphthamide was 7.5 μmol/L. For all compounds, the structure-activity relationships are discussed.     

Regioselective Hydrolysis of Cocaine and A Convenient Acylation Procedure by Benzoylecgonine

Regioselective hydrolysis of cocaine led, according to the reaction conditions, either to benzoylecgonine or to ecgonine methyl ester. Acylation with benzoylecgonine was readily achieved when benzotriazolyloxytrisdimethylamino-phosphonium (BOP) was used as a coupling agent.     

The chemical reactivity of a known anti-psoriasis drug. Part 1: Further insights into the products resulting from oxidative cleavage

The oxidative cleavage of the known anti-psoriasis drug 1 to give 2 has been reported previously. Due to the importance of accessing medium-sized ring containing systems via oxidative cleavage, this reaction has been revisited revealing additional information about the structure of 2. Alternative reaction products were identified when the reaction was carried out in the presence of water. The conversion of 1 to 2 has also been carried out using ruthenium tetroxide. A detailed variable temperature NMR and computational study of the restricted rotation of the N-aryl ring in 2 is presented.